Background

Evening primrose oil (EPO) contains an omega-6 essential fatty acid, gamma-linolenic acid (GLA), which is believed to be the active ingredient. EPO has been studied in a wide variety of disorders, particularly those affected by metabolic products of essential fatty acids. However, high-quality evidence for its use in most conditions is still lacking.

Evidence

DISCLAIMER:
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Atopic dermatitis (eczema):
There are several studies of evening primrose oil taken by mouth for eczema. Large well-designed studies are needed before a strong recommendation can be made. Evening primrose oil is approved for skin disorders in several countries outside of the United States.
Grade: B

Breast cancer:
Not enough information is available to advise the use of evening primrose oil for breast cancer. People with known or suspected breast cancer should consult with a qualified healthcare professional about possible treatments.
Grade: C

Breast cysts:
The limited available research does not demonstrate that evening primrose oil has a significant effect on treating breast cysts.
Grade: C

Breast pain (mastalgia):
Although primrose oil is used for breast pain in several European countries, high-quality human studies using this treatment are lacking. Therefore, the available information does not allow recommendation for or against the use of primrose oil in this condition.
Grade: C

Bronchitis:
There is evidence that primrose oil, in combination with thyme, may have some benefits in the treatment of acute bronchitis. However, it is unclear if primrose alone is useful in treating bronchitis. More studies are needed to examine the effectiveness of primrose oil alone as a therapy for bronchitis.
Grade: C

Chronic fatigue syndrome/post-viral infection symptoms:
Not enough information is available to advise the use of evening primrose oil for symptoms of chronic fatigue syndrome or fatigue following a viral infection.
Grade: C

Diabetes:
A small number of laboratory studies and theory suggests that evening primrose oil may be helpful in diabetes, but more information is needed before a firm recommendation can be made.
Grade: C

Diabetic neuropathy (nerve damage):
Gamma-linolenic acid (GLA), one of the components of evening primrose oil, may be helpful in people with diabetic neuropathy. Additional studies are needed before a strong recommendation can be made.
Grade: C

Multiple sclerosis (MS):
It is theorized that primrose oil may be helpful in patients with MS based on laboratory studies. Limited evidence is available in humans.
Grade: C

Obesity/weight loss:
Initial human study is unclear about the effects that evening primrose oil may have on weight loss.
Grade: C

Osteoporosis:
Primrose oil has been suggested as a possible treatment for bone loss/osteoporosis. However, osteoporosis studies using primrose oil as a treatment are lacking. Well-designed human trials are needed before primrose oil can be recommended for osteoporosis therapy.
Grade: C

Pre-eclampsia/high blood pressure of pregnancy:
Evening primrose oil is proposed to have effects on chemicals in the blood called prostaglandins, which may play a role in pre-eclampsia. However, more studies are needed before a firm conclusion can be drawn.
Grade: C

Raynaud's phenomenon:
Not enough scientific information is available to advise the use of evening primrose oil for Raynaud's phenomenon.
Grade: C

Rheumatoid arthritis:
Benefits of evening primrose oil in the treatment of arthritis have not clearly been shown. More information is needed before a firm recommendation can be made.
Grade: C

Scale-like dry skin (ichthyosis vulgaris):
Not enough scientific information is available to advise the use of evening primrose oil for dry skin.
Grade: C

Asthma:
Available evidence does not support the use of evening primrose oil as a treatment for asthma. Further research is needed to confirm this conclusion.
Grade: D

Menopause (flushing/bone metabolism):
Available studies do not show evening primrose oil to be helpful with these potential complications of menopause. More evidence of effectiveness is needed before primrose can be recommended as a treatment for menopausal symptoms.
Grade: D

Pre-menstrual syndrome (PMS):
Small human studies do not report that evening primrose oil is helpful for the symptoms of PMS.
Grade: D

Psoriasis:
Initial research does not show a benefit from evening primrose oil in the treatment of psoriasis.
Grade: D

Schizophrenia:
Results from studies of mixed quality do not support the use of evening primrose oil for schizophrenia. In contrast, fish oils have shown some promise in this disease, and further study is merited.
Grade: D

Dosing

Adults (18 years and older)

Studies in the treatment of eczema have used doses of 4 to 8 grams of evening primrose oil (EPO) daily, taken by mouth, divided into several smaller doses throughout the day. Studies treating breast pain have used doses of 3 grams EPO daily, taken by mouth, divided into several smaller doses throughout the day.

Children (younger than 18 years)

Studies in children treated for skin conditions have used 3 grams of evening primrose oil daily, taken by mouth, divided into several smaller doses throughout the day. It is reported that the maximum dose should not be greater than 0.5 gram per kilogram of body weight daily. Medical supervision is required.

Safety

DISCLAIMER:
Many complementary techniques are practiced by healthcare professionals with formal training, in accordance with the standards of national organizations. However, this is not universally the case, and adverse effects are possible. Due to limited research, in some cases only limited safety information is available.

Side Effects and Warnings

Several reports describe seizures in individuals taking evening primrose oil (EPO). Some of these seizures developed in people with a previous seizure disorder, or in individuals taking EPO in combination with anesthetics. Based on these reports, people with seizure disorders should not take EPO. EPO should be used cautiously with drugs used to treat mental illness such as chlorpromazine (Thorazine®), thioridazine (Mellaril®), trifluoperazine (Stelazine®), or fluphenazine (Prolixin®), due to an increased risk of seizure. Patients who plan to undergo surgery requiring anesthesia should stop taking EPO two weeks ahead of time because of the possibility of seizure.

Other reports describe occasional headache, abdominal pain, nausea, and loose stools in people taking EPO. In animal studies, gamma-linolenic acid (an ingredient of evening primrose oil) is reported to decrease blood pressure. Early results in human studies do not show consistent changes in blood pressure.

Pregnancy and Breastfeeding

There is not enough information to recommend the safe use of evening primrose oil during pregnancy or breastfeeding.

Interactions

Interactions with Drugs

Because of reported seizures in people taking evening primrose oil alone or in combination with certain medications used to treat mental illness, patients should use caution when combining evening primrose oil with medications like chlorpromazine (Thorazine®), thioridazine (Mellaril®), trifluoperazine (Stelazine®), or fluphenazine (Prolixin®). Individuals undergoing surgery requiring general anesthesia may be more sensitive to developing seizures, and should stop taking evening primrose oil two weeks ahead of time. In people with a history of seizures, doses of anti-seizure medications may require adjustment because evening primrose oil may increase the risk of seizures.

An ingredient of evening primrose oil, gamma-linolenic acid, is reported to lower blood pressure in animal studies. Although human studies do not show clear changes in blood pressure, people taking certain blood pressure medications should consult with a healthcare professional before starting evening primrose oil.

Possible additive effects may occur when primrose oil is taken with anticoagulants (blood thinners) and drugs used to treat arthritis.

Interactions with Herbs and Dietary Supplements

In animal studies, gamma-linolenic acid (an ingredient of evening primrose oil) is reported to lower blood pressure. Therefore, in theory, evening primrose oil may have effects on blood pressure, and should be used cautiously when combined with other agents that may lower blood pressure.

Theoretically, evening primrose oil may have additive effects when taken concomitantly with thyme, because a fixed combination of thyme fluid extract and primrose root tincture (Bronchicum Tropfen) has been used in studies to treat bronchitis.

Primrose oil may potentially interact with herbs and supplements used to treat arthritis, gastrointestinal disorders, obesity, seizures, viral infections, and psychosis. Primrose oil may interact with stimulants and herbs and supplements that are metabolized in the liver. Antineoplastics may also interact with primrose.

Bibliography

DISCLAIMER:
Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.